1. Technical Field
The present invention relates to a light source device, a monitor device, a projector, and a driving method for driving a light source device.
2. Related Art
A projection-type liquid crystal projector that uses a liquid crystal panel as a light valve and that will be an available means for projecting onto a large screen under development is flourishingly today.
In a projector of this type, a high luminance of a light source is required for reproduction of a bright picture.
However, actually, it is impossible to completely intercept light from a light source because a liquid crystal panel is used.
Thus, when displaying a real image, a black float caused by leaks of light or the like occurs depending on the increasing brightness of a light source. Therefore, increase of luminance in a light source does not always improve contrast of the image.
Furthermore, an increase of luminance in a light source brings a disadvantage from the viewpoint of a heat-resistant of liquid crystal panel. Especially, when a dark image is displayed on an entire screen via a liquid crystal panel, the amount of shading in the liquid crystal panel is large. Therefore, heat absorption in a liquid crystal panel or a polarization plate increases, and it is connected to damage of liquid crystal panels.
On the other hand, as suggested in Japanese Unexamined Patent Application, First Publication No. H06-160811, for example, a method for controlling contrast by varying the output of a light source based on a peak signal of an image, as a means that solves a black float depending on a high luminance of a light source and a problem in that damage occurs due to heat absorption in a liquid crystal panel, a polarization plate, or the like.
However, the metal halide lamp that is described in Japanese Unexamined Patent Application, First Publication No. H06-160811, has a problem in that the illumination color temperature that causes the output of a light source to vary is limited, in that the length of time of emission is short, in the impossibility of quick lighting and intermittent lighting, or the like.
Thus, a laser light source is expected as a light source overcoming the above-described problems.
However, each laser light source has each output characteristic, and there are differences between the output characteristics of each of the laser light sources. Particularly, the influences of the individual differences remarkably occur in the vicinity of the threshold level of each laser light source. Even if the same electricity is input to the laser light sources, a great difference in the output of each laser light source may occur.
Therefore, in order to vary the output from a light source in the case of using a plurality of laser lights, even if the electric current supply is continuously varied and the amount of laser light is controlled as disclosed in Japanese Unexamined Patent Application, First Publication No. H06-160811, the output (amount of light emitted) of each of the laser light sources is different from each other. As a result, there is a problem in that it is difficult to obtain a desired output (amount of light emitted).